It is now common practice in potato harvesting to employ automatic means to separate potatoes from soil and stones and to grade the crop by size. However, quality selection (that is, the removal of sub-standard potatoes from acceptable potatoes) has not been effectively automated and still relies upon operators picking out sub-standard potatoes as the crop passes along an inspection table. This quality procedure is inefficient in terms of labour deployment and is usually the speed-determining step in potato handling.
It has previously been proposed to improve operator efficiency by providing automatic removal means responsive to a position-indicating signal from a manually operable indicator. In said system, the indicator comprises an oscillating coil which is actuated when the indicator is pressed on a potato to be rejected and the position of said potato is indicated by a signal induced by an orthogonal array of coils disposed beneath the inspection table. Such a system has a number of inherent disadvantages, including the need to physically contact sub-standard potatoes and to carefully align potatoes on the table relative to said array because of lack of good resolution.